A number of anti-lock brake control systems have been developed for use for vehicle wheels, and are intended to prevent sudden locking of vehicle wheels during application of a brake to the vehicle wheels. Such sudden locking of the vehicle wheels may be avoided by detection of the rotational speed of a vehicle propeller shaft and the variation in the ratio of rotational speed to time. In the application of a brake, the value of pressure as varied is used for a control signal for controlling an actuator provided in the brake operating fluid system.
An anti-lock brake control system of the kind as above described mostly includes electronic circuits which serve to detect the variation of rotational speed and compare the value of varied pressure with a desired value. The system including electronic circuits practically involves many disadvantages such as complexity of circuitry, high cost and expense of its operation and maintenance.
An anti-lock brake control system using fluidic elements has been lately proposed in place of the electronic circuit, which is featured in that a sensor is provided in the control system which can vary pressure in a control fluid supplied to an operational circuit depending on the rotational speed and the vehicle speed. These sensors have been used practically but they have still many disadvantages in that, in most cases, the construction is very complicated and their performance is not excellent.